Polyesters stabilized with aromatic isocyanates

ABSTRACT

A THERMAL STABILIZED POLYESTER COMPRISING A HIGHLY POLYMERIC LINEAR POLYESTER CONTAINING A STABILIZING AMOUNT OF AN AROMATIC MONO- OR POLYISOCYANATE.

United States Patent Q POLYESTERS STABILIZED WITH AROMATIC ISOCYANATES Mary J. Stewart, Media, and John A. Price, Swarthmore, Pa., assignors to FM'C Corporation, Philadelphia, Pa. No Drawing. Filed June 5, 1968, Ser. No. 734,534

Int. Cl. C08g 51/60 U.S. Cl. 260-459 9 Claims ABSTRACT OF THE DISCLOSURE A thermal stabilized polyester comprising a highly polymeric linear polyester containing a stabilizing amount of an aromatic mono or polyisocyanate.

This invention relates to highly polymeric linear polyester resins that possess improved thermal stability and to a method of producing same.

The fiberand film-forming linear polyester resins used in the present invention, which are known as saturated linear polyesters, can be prepared by first carrying out a condensation reaction between an aromatic dicarboxylic acid or ester thereof which does not contain any ethylenic unsaturation and a suitable diol to form a prepolymer. The resulting prepolymer is then polycondensed to form the desired saturated linear polyester resin. When an ester of a dicarboxylic acid is used as the starting material, it is first reacted with a diol in the presence of a transesterification or ester-interchange catalyst by means of an ester-interchange reaction; whereas when a dicarboxylic acid is used as the starting material, it is first subjected to a direct esterification reaction with a diol in the presence of what is generally called a first stage additive or ether inhibitor. In either instance, the resulting reaction product, which may be generally described as a polyester prepolymer, is then polycondensed in the presence of a polycondensation catalyst to form a polyester resin.

For example, in the case of the transesterification method of preparing polyethylene terephthalate, ethylene glycol is reacted with dimethyl terephthalate to form a polyester prepolymer which is comprised mainly of bis- Z-hydroxyethyl terephthalate; or in the direct esterification method, ethylene glycol is reacted with terephthalic acid to form the resulting polyester prepolymer which is then polycondensed to form the desired polyester resin.

Linear polyester resins, such as polyethylene terephthalate and others, are widely used in the production of films and fibers and the like. However, it is generally known that such polyester products degrade when exposed to heat for a substantial period of time. Such degradation is particularly a problem in the extrusion and spinning processes of the finished resins to form the above-denoted products. Additionally, the fibers produced from such resins are extensively used in the textile field, and as a result of this application, are subjected to rather extreme temperatures in the processes of washing, drying, and ironing. Therefore, it is highly desirable that the polyester resin composition possess as much stability at high temperatures as possible.

Therefore, it is an object of the present invention to prepare a highly polymeric linear polyester resin composition which exhibits improved thermal stability.

Another object of the present invention is to provide a method of preparing linear polyester resin exhibiting such a high degree of thermal stability.

These and other objects are accomplished in accordance with the present invention with a stabilized polyester composition comprising a highly polymeric linear polyester containing a stabilizing amount of an organic aromatic monoor polyisocyanate, or any combination thereof.

In the practice of the present invention, any of the well-known and commercially available organic aromatic monoor polyisocyanates may be employed as a thermal stabilizer. This includes mono-, di-, tri-, and tetraisocyanates. For example, among the wide variety of aromatic polyisocyanates that can be used are metaphenylene diisocyanate, para-phenylene diisocyanate, para-para'-diphenyl diisocyanate, diphenyl-3,3-dimethyl-4,4'-diisocyanate, diphenyl-3,3'-dimethoxy-4,4diisocyanate, 1,5-naphthalene diisocyanate, diphenylmethane-4,4'-diisocyanate, toluene-2,4-diisocyanate, para-tolyl-isocyanate, triphenylmethane triisocyanate, toluene-2,4,6-triisocyanate, benzene-1,3,S-triisocyanate, and 4,4-dimethyldiphenylmethane-2,2',5,5'-tetraisocyanate.

The highly polymeric linear polyester resins used in the preparation of the subject thermal stabilized polyester compositions can be prepared via either the conventional ester-interchange reaction or direct esterification method, both of which are thoroughly disclosed throughout the prior art.

In accordance with the present invention, it has been found that it is preferable and most convenient to thoroughly mix or blend the monoor polyisocyanate stabilizer into the highly polymeric filamentor film-forming polyester resin immediately after the polycondensation step has been completed, at atmospheric pressure while the resin is still molten, in order to form a uniform blend of the polyester resin and thermal stabilizer. Obviously, such stabilizers can also be incorporated in highly polymeric polyester resins at any time after their polycondensation has been completed-by merely remelting the resin and stirring in a monoor polyisocyanate stabilizer. The term highly polymeric filament and film-forming polyester resin, as used herein, denotes polyester resins having an intrinsic viscosity no less than about 0.60, as measured in a 60% phenol-40% tetrachloroethane solution, wt./wt., at 30 C.

It has been found that the present thermal stabilizers, as defined above, are effective as such in polyester resin compositions when employed in amounts ranging from about 0.01% to about 0.5%, by weight, based on the 'Weight of the linear polyester resin. Usually, it has been found that concentrations ranging from about 0.02% to about 0.3%, by weight, are preferred in most instances. However, when indicated, concentrations less or greater than the above can be used, but their effectiveness is generally reduced proportionally.

The relative effectiveness of compounds as thermal stabilizers in polyester compositions can be most accurately expressed on the basis of percent broken bonds resulting from exposing a given resin composition containing such a stabilizer to elevated temperatures for a given period, rather than from a direct reading of the difference between the original or initial intrinsic viscosity and the final or degraded intrinsic viscosity of such a resin composition. It is known and logically expected that polyester polymers having higher original intrinsic viscosities will generally show a greater drop in intrinsic viscosity when exposed to elevated temperatures than those with lower original intrinsic viscosities, although on a percent broken bonds basis, the stability of such a resin composition having a higher original intrinsic viscosity might be equivalent to one exhibiting a lesser drop in intrinsic viscosity.

The percent broken bonds value, as determined for polyethylene terephthalate, is defined as the bonds broken ice 3 per mole of ethylene terephthalate times 100, and the values given hereinbelow in the following examples were calculated by the use of the following equation:

I/a l/a Percent, broken bonds=[(%) 9.6 10 5 The value of K and a may be found in the literature, such as Conix, A., Makromol., Chemie 26, p. 226 (1958), wherein K=0.00021 and a=0.82. V: in the above formula is the degraded or final intrinsic viscosity value and V is the original or initial intrinsic viscosity value.

For purposes of obtaining original or initial intrinsic viscosity values for insertion in the above equation, the original intrinsic viscosity values of the polyester resin products were obtained by measuring the intrinsic viscosities of the resin compositions as produced. The degraded intrinsic viscosity values for insertion in the above equation were determined by the following procedure: The polyester resin composition was ground and passed through a U.S.S. mesh screen and dried at 120 C. in vacuo for 16 hours, then cooled in a desiccator. Two to three grams of this dried resin was then placed in a test tube which was then inserted into an aluminum block preheated to 280 C. (:05 C.). The block was then sealed and evacuated to 0.1 mm. of mercury. After holding for about 10-15 seconds, the block was filled with dried, oxygen-free nitrogen gas. This vacuum-nitrogen purge was then repeated for a total of three times; the entire process took 5-7 minutes. Then, the resin sample was left in the heated block for an additional two :hours under a slow stream of nitrogen. After this two-hour period, the resin sample was removed from the block and placed in a desiccator which was first evacuated and then filled with nitrogen. The intrinsic viscosity of the resin product was then determined and such anintrinsic viscosity value is noted as the degraded intrinsic viscosity.

All of the intrinsic viscosity determinations of the polyester resin products produced in the examples below were determined ha 60% phenol 40% tetrachloroethane solution, wt./wt., at 30 C., according to conventional laboratory procedure. The other analytical data given was determined by conventional laboratory procedures.

EXAMPLE I A blended mixture comprising 474 g. of terephthalic acid, 288 mls. of ethylene glycol and 149 mls. of triethylamine was charged into a reaction vessel equipped with a nitrogen inlet, a Dean-Starke separating apparatus, heating means and stirring means. The reaction mixture was agitated and the temperature was raised to about 197 C. under a nitrogen blanket at atmospheric pressure. At about 190 C., a water-triethylamine azeotropic mixture started to distill off. The azetropic mixture was continuously separated by means of the Dean-Starke apparatus, and the triethylamine recovered was continuously returned to the reaction vessel. The reaction mixture became almost clear. Then, the temperature was allowed to rise to about 230 C. over a one-hour period to remove all the triethylamine and any excess glycol. The prepolymer product was allowed to cool under an atmosphere of nitrogen.

EXAMPLE II Fifty grams of the prepolymer product of Example I was mixed with 0.02 g. of antimony sec-butoxide and placed in a reaction vessel. The reaction mixture was heated at about 280 C. under a residual nitrogen reduced atmosphere of from about 0.05 to about 0.1 mm. of mercury while under agitation for about 2 hours to bring about the polycondensation of the polyester prepolymer and formation of a filamentand film-forming polyester resin having an original intrinsic viscosity of 0.88 and a melting point of 263 C. The degraded intrinsic viscosity was determined as 0.69, and the percent broken bonds of this polyethylene terephthalate resin composition per the above-defined testing procedures and equation was calculated as 0.132%.

EXAMPLE III Fifty grams of the prepolymer product of Example I was mixed with 0.02 g. of antimony sec-butoxide and placed in a reaction vessel. The reaction mixture was heated at about 280 C. under a residual nitrogen reduced atmosphere of from about 0.05 to about 0.1 mm. of mercury while under agitation for about 2 hours to bring about the polycondensation of the prepolymer and formation of a polyester resin as in Example H. After the polycondensation reaction had been completed, 0.02 cc. of triphenylmethane triisocyanate was thoroughly stirred into the polyester resin while still molten at atmospheric pressure, after which the filamentand film-forming resin product was cooled. The resin product had an original intrinsic viscosity of 0.79, and a melting point of 267 C. The degraded intrinsic viscosity was determined as 0.72, and the percent broken bonds of this polyethylene terephthalate resin composition per the above-defined testing procedures and equation was calculated as 0.050%.

EXAMPLE IV Fifty grams of the prepolymer product of Example I was mixed with 0.02 g. of antimony sec-butoxide and placed in a reaction vessel. The reaction mixture was heated at about 280 C. under a residual nitrogen reduced atmosphere of from about 0.05 to about 0.1 mm. of mercury while under agitation for about 2 hours to bring about the polycondensation of the prepolymer and formation of a polyester resin as in Example II. After the polycondensation reaction had been completed, 0.02 g. of diphenylmethane-4.4'-diisocyanate was thoroughly stirred into the polyester resin while still molten at atmospheric pressure, after which the filamentand film-forming resin product was cooled. The resin product had an original intrinsic viscosity of 0.81, and a melting point of 265 C. The degraded intrinsic viscosity was determined as 0.72, and the percent broken bonds of this polyethylene terephthalate resin composition per the above-defined testing procedures and equation was calculated as 0.061%.

EXAMPLE V Fifty grams of the prepolymer product of Example I was mixed with 0.02 g. of antimony sec-butoxide and placed in a reaction vessel. The reaction mixture was heated at about 280 C. under a residual nitrogen reduced atmosphere of from about 0.05 to about 0.1 mm. of mercury while under agitation for about 2 hours to bring about the polycondensation of the prepolymer and formation of a polyester resin as in Example II. After the polycondensation reaction had been completed, 0.02 g. of 3,3-dimethoxy-4,4'-biphenyl diisocyanate was thoroughly stirred into the polyester resin while still molten at atmospheric pressure, after which the filamentand film-forming resin product was cooled. The resin product had an original intrinsic viscosity of 0.70, and a melting point of 264 C. The degraded intrinsic viscosity was determined as 0.68, and the percent broken bonds of this polyethylene terephthalate resin composition per the above-defined testing procedures and equation was calculated as 0.022%

EXAMPLE VI Fifty grams of the prepolymer product of Example I was mixed with 0.02 g. of antimony sec-butoxide and placed in a reaction vessel. The reaction mixture was heated at about 280 C. under a residual nitrogen reduced atmosphere of from about 0.05 to about 0.1 mm. of mercury while under agitation for about 2 hours to bring about the polycondensation of the prepolymer and formation of a polyester resin as in Example II. After the polycondensation reaction had been completed, 0.02 cc. of p-tolyl isocyanate was thoroughly stirred into the polyester resin while still molten at atmospheric pressure, after which the filamentand film-forming resin product was cooled. The resin product had an original intrinsic viscosity of 0.69, and a melting point of 264 C. The degraded intrinsic viscosity was determined as 0.63, and the percent broken bonds of this polyethylene terephthalate resin composition per the above-defined testing procedures and equation was calculated as 0.056%.

EXAMPLE VII A mixture comprising 600 g. of dimethyl terephthalate, 396 mls. of ethylene glycol, and 0.24 g. of lithium hydride was charged into a reaction vessel equipped with a nitrogen inlet, heating means and stirring means. The reaction mixture was agitated and heated at atmospheric pressure at 198 C. under a nitrogen blanket. The reaction mixture was held at about 198 C. for about two hours, during which time by-product methyl alcohol was distilled off. Then, the temperature of the reaction mixture was allowed to rise to 230 C. over a period of about one hour to distill off any remaining by-product methyl alcohol and ethylene glycol and form a polyester prepolymer. The prepolymer product was allowed to cool under an atmosphere of nitrogen.

EXAMPLE VIII Fifty grams of the prepolymer product of Example VII was mixed with 0.02 g. of antimony trioxide and placed in a reaction vessel. The reaction mixture was heated at about 280 C. under a residual nitrogen reduced atmosphere of from about 0.05 to about 0.1 mm. of mercury while under agitation for about 2 hours to bring about the polycondensation of the prepolymer and formation of a polyester resin. The polyester resin formed had an original intrinsic viscosity of 0.81, and a melting point of 260 C. The degraded intrinsic viscosity was determined as 0.68, and the percent broken bonds of this polyethylene terephthalate resin composition per the above-defined testing procedures and equation was calculated as 0.094%.

EXAMPLE IX Fifty grams of the prepolymer product of Example VII was mixed with 0.02 g. of antimony trioxide and placed in a reaction vessel. The reaction mixture was heated at about 280 C. under a residual nitrogen reduced atmosphere of from about 0.05 to about 0.1 mm. of mercury while under agitation for about 2 hours to bring about the polycondensation of the prepolymer and formation of a polyester resin, as in Example VIII. After the polycondensation had been completed, 0.02 g. of 3,3-dimethoxy-4,4'-biphenyl diisocyanate was thoroughly stirred into the polyester resin while still molten at atmosphereic pressure, after which the filamentand film-forming resin product was cooled. The resin produced had an original intrinsic viscosity of 0.79, and a melting point of 261 C. The degraded intrinsic viscosity was determined as 0.68, and the percent broken bonds of this polyethylene terephthalate resin composition per the above-defined testing procedures and equation was calculated as 0.083%.

The results in the above examples indicate that the present monoor polyisocyanate stabilizers, when added to linear polyester resins, act to stabilize or reduce the degradation elfects of higher temperatures upon such resins. The change in intrinsic viscosity or the dilference between the original intrinsic viscosity and the degraded intrinsic viscosity is a direct measure of the heat stabilizing eifect that the present thermal stabilizers have upon polyester resins, and can be readily calculated from the above results.

When the controls above, Example II and VIII, are compared with their corresponding examples wherein the same catalyst systems and starting materials were used, but with the addition of a thermal stabilizer of the present invention, it can readily be seen from the intrinsic viscosity values and the percent broken bonds values that the present stabilizers act to limit the amount of degradation that takes place when polyester resin products are exposed to elevated temperatures for prolonged periods of time.

The present invention has been illustrated with particular respect to the stabilization of polyethylene terephthalate. However, the present thermal stabilizers are also eifective in stabilizing any fiberand film-forming linear polyesters and copolyesters; for example, those derived from aromatic dicarboxylic acids, such as isophthalic acid, and 4,4'-diphenyldicarboxylic acid, or ester derivatives thereof, and suitable diols, such as glycols of the series HO(CH OH, where n is 2 to 10.

We claim:

1. A thermal stabilized polyester composition comprising the product formed by incorporating from about 0.1 to 0.5% by weight of an aromatic monoor polyisocyanate or combination thereof into a molten saturated linear polyester resin.

2. The composition of claim 1 wherein the polyester is polyethylene terephthalate.

3. The composition of claim 1 wherein the monopolyisocyanate is 1,5-naphthalene diisocyanate.

4. The composition of claim 1 wherein the monopolyisocyanate is triphenylmethane triisocyanate.

5. The composition'of claim 1 wherein the monopolyisocyanate is diphenylmethane-4,4-diisocyanate.

6. The composition of claim 1 wherein the monoor polyisocyanate is 3,3'-dimethoxy-4,4'-bipheny1 diisocyanate.

7. The composition of claim 1 wherein the monoor polyisocyanate is p-tolyl isocyanate.

8. The composition of claim 1 wherein the monoor polyisocyanate is 4,4-dimethyl-diphenylmethane-2,2',5,5- tetraisocyanate.

9. The composition of claim 1 wherein the monoor polyisocyanate is meta-phenylene diisocyanate.

References Cited UNITED STATES PATENTS 2,578,653 12/1951 Goppel et a1 260-45 .9 3,226,368 12/1965 Perschl et al. 260-45.9 3,297,726 1/ 1967 Zecher et al 26045;9 3,401,144 9/1968 Britain 260-459 3,403,128 9/ 1968 Monhem et a1. 260-459 HOSEA E. TAYLOR, Primary Examiner US. Cl. X.R. 260 

